1. Field of the Invention
The invention concerns a device and process for an antenna array with switchable wide angle or directional characteristic, comprised of individual antennas for increasing the directional resolution and angular coverage, in the sense of monopulse-antenna, of which the total antenna mean radiation pattern or directional characteristic is characterized by a sum diagram and a differential diagram, wherein the individual antennas are connected via a network of phase-shifters or hybrid junctions, wherein the antenna array includes a sum input for selecting the individual antennas, so that the antenna mean radiation pattern or directional characteristic exhibits a sum diagram, and wherein the antenna array includes a differential input for selecting the individual antennas so that the antenna mean radiation pattern or directional characteristic exhibits a differential diagram.
In automobile short-range sensor technology, as well as in mobile communications, there is an increasing demand for sector-wide coverage of large angle areas. This problem is presently addressed by the employment of separate individual antennas respectively serving sectors. If the antenna characteristic (this term being used herein to mean aerial radiation pattern or directional characteristic) is to be switchable and/or adaptively adjustable, or, as the case may be, if for space saving or aesthetic reasons a large number of individual antennas is not appropriate, then antenna arrays must be employed. In the case of large main lobe breadths and large slewing angles, the slewing angle which can be realized is strongly limited on the basis of strongly increasing “grating-lobes”.
2. Description of the Related Art
The conventional technique for solving this problem involves employment of conformal, or angle preserving, array antennas. Such antennas presently remain in part in the research stage or are still too expensive for employment in series production.
From U.S. Pat. No. 4,044,359 a device is known, which is designed for suppressing interfering signals. Herein, by the targeted interaction of two antenna systems, directional information is obtained, which is subsequently used for improved suppression of interfering transmissions.
In the reference by Kuga et al. (Kuga, Nobuhiro et al., Beam-Switched planar array antenna for mobile communications, Electronics and Communications in Japan, Part 1, Vol. 81, No. 3, 1998, pp 57-63) an antenna array with large angle coverage is described, wherein the individual angular distributions are covered by means of the switchable arrangement of antenna groups, which exhibit two switchable antenna characteristics respectively offset by 180°. For example, herein two antenna groups arranged at right-angles to each other are shown, wherein these four segments cover an angle area of 360°.
Patent publication DE 27 09 758 B2 shows an emitter group arranged in a circular shape for finding the azimuthal direction. Herein already multiple antennas lying along a segment of a circle are assembled into an emitter group and driven via a circuit matrix network. These individual emitter groups are driven in the sense of a monopulse antenna, which utilizes a sum diagram and one single differential diagram. The high angular resolution of the antenna array is herein achieved by suitable arrangement (here circular shaped, for angle coverage of 360°) of the individual emitter groups and by the comparison of the respective received signals with each other.
In the literature, Skolnik (Skolnik, M., Radar Handbook, 2nd ed., McGraw-Hill Inc., New York) describes diverse antenna arrays which are suitable for operation as monopulse antennas (see in particularly p. 6.24, table 6.1). It is herein however presumed according to FIG. 6.19 (p. 6.23), that the antenna arrays utilize one sum and one individual differential characteristic. As for the particularly noteworthy feature, reference is made to the problem arising with respect to the directional effect of the antenna characteristic, which is based upon the fact that during the dimensioning of the antenna a compromise must be found between the efficiency of the summation characteristic of the antenna and the differential characteristic of the antenna.
The conference handout of Hannan (Hannan, P., Loth, P., A Monopulse Antenna Having Independent Optimization of the Sum and Difference Modes, IRE Int. Conv. Rec., pt.1, March 1961) concerns the problem of finding an optimal compromise with respect to the efficiency of sum and differential characteristics of the antenna diagram. For this, an antenna array is described, which is comprised of individual antennas, which are connected with each other at a fixed phase relationship via coupling with a network comprised of a hybrid junctions. In this manner it is achieved that the angle area of the emission lobe of the differential characteristic is efficiently narrowed.
The selection schematics which can be found in the literature are always based on the presumption that there will always be two groups of antenna elements provided next to each other and arranged counter-phasic to each other.